Switch circuit capable of overcurrent protection with small and simple circuit, and with simple operation, without affecting normal operation

ABSTRACT

A driver circuit controls a first switch element. A first resistor is connected between the driver circuit and the first switch element. A second switch element is connected to the first switch element. An overcurrent detector circuit controls the second switch element based on an overcurrent current flowing through the first switch element. A second resistor is connected between the overcurrent detector circuit and the second switch element. The first and second resistor is set such that a turn-off time of the first switch element when the second switch element is turned on by the overcurrent detector circuit is longer than a turn-off time of the first switch element when the first switch element is turned off by the driver circuit.

CROSS REFERENCE TO RELATED APPLICATIONS

This is the U.S. national stage of application No. PCT/JP2019/009733,filed Mar. 11, 2019. Priority under 35 U.S.C. § 119(a) and 35 U.S.C. §365(b) is claimed from Japanese Application No. 2018-140092, filed Jul.26, 2018, the disclosure of which is also incorporated herein byreference.

TECHNICAL FIELD

The present disclosure relates to a switch circuit including switchelements and a control circuit thereof, and also relates to a powerconverter apparatus including at least one such switch circuit.

BACKGROUND ART

Conventionally, switching power supply apparatuses with overcurrentprotection have been known as disclosed in, for example, PatentDocuments 1 and 2.

Patent Document 1 discloses a gate driver circuit for a voltage-drivensemiconductor element used in a power converter apparatus. In this gatedriver circuit, a series-connected circuit of first and second resistorsis connected between a signal output terminal of a signal insulator, andcontrol terminals of semiconductor elements connected to a gate terminalof the voltage-driven semiconductor element, the semiconductor elementsbeing complementarily operable to flow a gate current of thevoltage-driven semiconductor element. A switch element is connectedbetween a connection point connecting the first resistor to the secondresistor, and an emitter terminal of the voltage-driven semiconductorelement, the switch element being turned on in order to forcibly turnthe voltage-driven semiconductor element off when an overcurrent flowsthrough the voltage-driven semiconductor element. Further, a capacitoris connected between a connection point connecting the second resistorto control terminals of the semiconductor elements, and an emitterterminal of the voltage-driven semiconductor element.

Patent Document 2 discloses a single-ended forward switching powersupply apparatus having an overcurrent protection function and includinga synchronous rectifier circuit. This switching power supply apparatusis provided with: a main switching element, a current detector circuit,a PWM control circuit, a variable resistor element, and a variablecontrol circuit, on a primary side of a main transformer. The currentdetector circuit detects a switching current flowing through the mainswitching element. The PWM control circuit controls ON and OFF of themain switching element, receives an output signal of the currentdetector circuit, and shortens an ON time of the main switching elementwhen a peak value of the switching current reaches a first referencevalue. The variable resistor element is connected between gate andsource terminals of the main switching element. The variable controlcircuit receives the output signal of the current detector circuit,compares the peak value of the switching current with a second referencevalue at each switching period, and when the switching current reachesthe second reference value, reduces a resistance of the variableresistor element so as not to increase a voltage between the gate andsource terminals of the main switching element, thus preventing anincrease in the peak value of the switching current.

CITATION LIST Patent Documents

-   PATENT DOCUMENT 1: Japanese Patent Laid-open Publication No. JP    2007-104805 A-   PATENT DOCUMENT 2: Japanese Patent No. JP 5571594 B

SUMMARY OF INVENTION Technical Problem

According to the gate driver circuit of Patent Document 1, manycomponents for overcurrent protection are connected between the signalinsulator and the voltage-driven semiconductor element. Due to such manycomponents, the circuit's scale and cost increase. The increase in thecircuit's scale results in an increase in inductance. On the other hand,driver circuits for next-generation high-speed power semiconductorelements, including super junction MOSFET (SJMOS), SiC, GaN, etc., needto have low inductance so as to reduce driving noise. Accordingly, inorder to reduce the cost and also reduce the inductance, it is necessaryto achieve overcurrent protection with a circuit smaller and simplerthan that of the prior art.

In addition, according to the gate driver circuit of Patent Document 1,the semiconductor elements operable complementarily are provided betweenthe switch element for overcurrent protection and the voltage-drivensemiconductor element. Due to the presence of these semiconductorelements, when an overcurrent in the voltage-driven semiconductorelement is detected, a delay occurs from turning on of the switchelement for overcurrent protection, to turning off of the voltage-drivensemiconductor element. Accordingly, in order to shorten an operatingtime from detection of an overcurrent to protection against theovercurrent, it is necessary to achieve overcurrent protection with acircuit smaller and simpler than that of the prior art.

In addition, according to the gate driver circuit of Patent Document 1,turning on or off of the voltage-driven semiconductor element isfollowed by charging or discharging of the capacitor for a timedepending on a time constant of the second resistor and the capacitor,and the charging or discharge time results in a delay in an operation ofthe voltage-driven semiconductor element. This delay occurs not onlywhen detecting the overcurrent in the voltage-driven semiconductorelement and protecting the voltage-driven semiconductor element from theovercurrent, but also during a normal operation of the voltage-drivensemiconductor element. Thus, a switching speed of the voltage-drivensemiconductor element during the normal operation is slowed, and a lossincreases. Accordingly, it is necessary to achieve overcurrentprotection without affecting the normal operation.

In addition, according to the switching power supply apparatus of PatentDocument 2, when an overcurrent in the main switching element isdetected, two-stage overcurrent protection is performed: preventing theincrease in the peak value of the switching current by the variablecontrol circuit and the variable resistor element, and then, blockingthe switching current by the PWM control circuit. By performing thetwo-stage operation, a delay occurs from detection of an overcurrent toprotection against the overcurrent. Accordingly, in order to shorten theoperating time from detection of an overcurrent to protection againstthe overcurrent, it is necessary to achieve overcurrent protection witha circuit and an operation simpler than those of the prior art.

An object of the present disclosure is to provide a switch circuitincluding switch elements and a control circuit thereof, the switchcircuit being capable of achieving overcurrent protection with a circuitsmaller and simpler than that of the prior art, and with an operationsimpler than that of the prior art, without affecting a normaloperation. In addition, another object of the present disclosure is toprovide a power converter apparatus including at least one such switchcircuit.

Solution to Problem

In order to solve the above-mentioned problem, a switch circuit and apower converter apparatus according to aspects of the present disclosureare configured as follows.

A switch circuit according to an aspect of the present disclosure isprovided with: a first switch element, a driver circuit, a firstresistor, a second switch element, an overcurrent detector circuit, anda second resistor. The first switch element has a first terminalconnected to a first voltage source, a second terminal connected to asecond voltage source, and a third terminal. The driver circuit thatgenerates a first control signal for turning the first switch element onand off. The first resistor is connected between the driver circuit andthe third terminal. The second switch element has a fourth terminalconnected to the third terminal, a fifth terminal connected to thesecond voltage source, and a sixth terminal. The overcurrent detectorcircuit generates a second control signal for turning the second switchelement on and off, based on whether or not a current flowing throughthe first switch element exceeds a predetermined threshold. The secondresistor is connected between the overcurrent detector circuit and thesixth terminal. The first and second resistors have resistances set suchthat a turn-off time of the first switch element when the second switchelement is turned on by the second control signal is longer than aturn-off time of the first switch element when the first switch elementis turned off by the first control signal.

In this case, “the first switch element” is a power semiconductorelement to which a voltage of the first voltage source is applied, andwhich passes and blocks a current from the first voltage source. Inaddition, “the second switch element” turns the first switch element offusing soft turn-off when detecting an overcurrent in the first switchelement. The “soft turn-off” means changing a signal level of a controlsignal to be applied to a switch element, when turning the switchelement off.

The second switch element, the overcurrent detector circuit, and thesecond resistor constitute an overcurrent protection circuit for thefirst switch element, the overcurrent protection circuit detecting anovercurrent in the first switch element, and protecting the first switchelement from the overcurrent. In addition, the driver circuit, the firstresistor, the second switch element, the overcurrent detector circuit,and the second resistor constitute a control circuit for the firstswitch element, the control circuit turning the first switch element onand off, detecting an overcurrent in the first switch element, andprotecting the first switch element from the overcurrent.

Since the switch circuit according to the aspect of the presentdisclosure is configured as described above, it is possible to achieveovercurrent protection with a circuit smaller and simpler than that ofthe prior art, and with an operation simpler than that of the prior art,without affecting a normal operation.

The switch circuit according to the aspect of the present disclosure maybe further provided with a capacitor that is connected between the fifthand sixth terminals of the second switch element.

Since the switch circuit according to the aspect of the presentdisclosure is provided with the capacitor, a malfunction of the secondswitch element due to a mirror current is less likely to occur.

In the switch circuit according to the aspect of the present disclosure,when turning the second switch element off, the overcurrent detectorcircuit may generate the second control signal having a polarityopposite to a polarity of an electric potential of the first voltagesource, with respect to an electric potential of the second voltagesource.

Since the switch circuit according to the aspect of the presentdisclosure generates the second control signal as described above, amalfunction of the second switch element due to a mirror current is lesslikely to occur.

In the switch circuit according to the aspect of the present disclosure,the first resistor may be integrated with the driver circuit.

Since the switch circuit according to the aspect of the presentdisclosure is configured as described above, it is possible to furtherreduce the size of the switch circuit and simplify the switch circuit.

In the switch circuit according to the aspect of the present disclosure,the second switch element may be an NPN transistor or an N-channelMOSFET. The overcurrent detector circuit may set the second controlsignal to a high level when the current flowing through the first switchelement exceeds the threshold, and set the second control signal to alow level when the current flowing through the first switch element isequal to or smaller than the threshold.

In the switch circuit according to the aspect of the present disclosure,the second switch element is a PNP transistor or a P-channel MOSFET. Theovercurrent detector circuit may set the second control signal to a lowlevel when the current flowing through the first switch element exceedsthe threshold, and set the second control signal to a high level whenthe current flowing through the first switch element is equal to orsmaller than the threshold.

Since the switch circuit according to the aspect of the presentdisclosure is configured as described above, the overcurrent detectorcircuit can be appropriately selected according to the specifications ofthe second switch element, and the second switch element can beappropriately selected according to the specifications of theovercurrent detector circuit.

A power converter apparatus according to an aspect of the presentdisclosure is provided with at least one of the switch circuit accordingto the aspect of the present disclosure.

Since the power converter apparatus according to the aspect of thepresent disclosure is configured as described above, it is possible toachieve overcurrent protection with a circuit smaller and simpler thanthat of the prior art, and with an operation simpler than that of theprior art, without affecting a normal operation.

Advantageous Effects of Invention

According to the present disclosure, it is possible to provide theswitch circuit capable of achieving overcurrent protection with acircuit smaller and simpler than that of the prior art, and with anoperation simpler than that of the prior art, without affecting a normaloperation.

In addition, according to the present disclosure, it is possible toprovide a power converter apparatus including at least one such switchcircuit.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit 40 according to a first embodiment.

FIG. 2 is a waveform diagram schematically illustrating an exemplaryoperation of the switch circuit 40 of FIG. 1 during a normal operation.

FIG. 3 is a waveform diagram schematically illustrating an exemplaryoperation of the switch circuit 40 of FIG. 1 when detecting anovercurrent.

FIG. 4 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit according to a comparison example.

FIG. 5 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit 40A according to a first modifiedembodiment of the first embodiment.

FIG. 6 is a circuit diagram schematically illustrating an exemplaryconfiguration of the switch circuit 40A of FIG. 5 for simulationthereof.

FIG. 7 is a waveform diagram schematically illustrating an exemplaryoperation of the switch circuit of FIG. 6.

FIG. 8 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit 40B according to a second modifiedembodiment of the first embodiment.

FIG. 9 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit 40C according to a third modifiedembodiment of the first embodiment.

FIG. 10 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit 40D according to a fourth modifiedembodiment of the first embodiment.

FIG. 11 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit 40E according to a fifth modifiedembodiment of the first embodiment.

FIG. 12 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit 40F according to a sixth modifiedembodiment of the first embodiment.

FIG. 13 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit 40G according to a seventh modifiedembodiment of the first embodiment.

FIG. 14 is a block diagram schematically illustrating an exemplaryconfiguration of a power system according to a second embodiment.

FIG. 15 is a block diagram schematically illustrating an exemplaryconfiguration of a power converter apparatus 21 of FIG. 14.

FIG. 16 is a block diagram schematically illustrating an exemplaryconfiguration of a power converter apparatus 22 of FIG. 14.

FIG. 17 is a block diagram schematically illustrating an exemplaryconfiguration of a power converter apparatus 24 of FIG. 14.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments according to an aspect of the presentdisclosure (hereinafter, also referred to as “the present embodiment”)will be described with reference to the drawings. In the drawings, thesame reference characters indicate similar components.

First Embodiment

A switch circuit according to a first embodiment will be described withreference to FIGS. 1 to 13.

Exemplary Configuration of First Embodiment

FIG. 1 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit 40 according to the first embodiment.The switch circuit 40 of FIG. 1 is provided with: a switch element SW1,a driver circuit 1, a resistor R1, a switch element SW2, an overcurrentdetector circuit 2, and a resistor R2. The switch element SW2, theovercurrent detector circuit 2, and the resistor R2 constitute anovercurrent protection circuit for the switch element SW1, theovercurrent protection circuit detecting an overcurrent in the switchelement SW1, and protecting the switch element SW1 from the overcurrent.In addition, the driver circuit 1, the resistor R1, the switch elementSW2, the overcurrent detector circuit 2, and the resistor R2 constitutea control circuit 30 for the switch element SW1, the control circuit 30turning the switch element SW1 on and off, detecting an overcurrent inthe switch element SW1, and protecting the switch element SW1 from theovercurrent.

The switch element SW1 has a drain terminal D connected to a voltagesource VDD, a source terminal S connected to a ground GND, and a gateterminal G. The switch element SW1 is a power semiconductor element towhich a voltage of the voltage source VDD is applied, and which passesand blocks a current from the voltage source VDD. The switch element SW1is an N-channel MOSFET. An electric potential of the voltage source VDDis higher than an electric potential of the ground GND.

The switch element SW1 is, herein, also referred to as a “first switchelement”. In addition, herein, the drain terminal D of the switchelement SW1 is also referred to as a “first terminal”, the sourceterminal S thereof is also referred to as a “second terminal”, and thegate terminal G thereof is also referred to as a “third terminal”. Inaddition, herein, the voltage source VDD is also referred to as a “firstvoltage source”, and the ground GND is also referred to as a “secondvoltage source”. The voltage sources VDD and ground GND are examples ofthe “first voltage source” and the “second voltage source”,respectively. In addition, the switch element SW1 which is an N-channelMOSFET is an example of the “first switch element”.

The driver circuit 1 generates a control signal PWM_out for turning theswitch element SW1 on and off with a certain duty cycle. For example, aPWM signal is inputted from a previous-stage circuit (not shown) to thedriver circuit 1, and the driver circuit 1 generates and outputs acontrol signal PWM_out based on the PWM signal. When the switch elementSW1 is an N-channel MOSFET as described above, the control signalPWM_out becomes a high level when turning the switch element SW1 on, andthe control signal PWM_out becomes a low level when turning the switchelement SW1 off.

The control signal PWM_out is, herein, also referred to as a “firstcontrol signal”.

The resistor R1 is connected between the driver circuit 1 and the gateterminal G of the switch element SW1.

The resistor R1 is, herein, also referred to as a “first resistor”.

The switch element SW2 has a drain terminal D connected to the gateterminal G of the switch element SW1, a source terminal S connected to aterminal having the same electric potential as the electric potential ofthe source terminal S of the switch element SW1 (in the example of FIG.1, the ground GND), and a gate terminal G. The switch element SW2 turnsthe switch element SW1 off using soft turn-off when detecting theovercurrent in the switch element SW1. The switch element SW2 is anN-channel MOSFET.

The switch element SW2 is, herein, also referred to as a “second switchelement”. In addition, herein, the drain terminal D of the switchelement SW2 is also referred to as a “fourth terminal”, the sourceterminal S thereof is also referred to as a “fifth terminal”, and thegate terminal G thereof is also referred to as a “sixth terminal”. Theswitch element SW2 which is the N-channel MOSFET is an example of the“second switch element”.

The overcurrent detector circuit 2 generates a control signal DET_oc forturning the switch element SW2 on and off, based on whether or not acurrent flowing through the switch element SW1 exceeds a predeterminedthreshold Ith. In order to detect the overcurrent flowing through theswitch element SW1, the switch circuit 40 of FIG. 1 is further providedwith a current detector CT. The current detector CT is, for example, acurrent transformer. In a case where the switch element SW2 is theN-channel MOSFET as described above, the overcurrent detector circuit 2sets the control signal DET_oc to a high level when the current flowingthrough the switch element SW1 exceeds the threshold Ith, and sets thecontrol signal DET_oc to a low level when the current flowing throughthe element SW1 is equal to or smaller than the threshold Ith.

The control signal DET_oc is, herein, also referred to as a “secondcontrol signal”.

The resistor R2 is connected between the overcurrent detector circuit 2and the gate terminal G of the switch element SW2.

The resistor R2 is, herein, also referred to as a “second resistor”.

The resistors R1 and R2 have resistances set such that a turn-off timeT2 of the switch element SW1 when the switch element SW2 is turned on bythe control signal DET_oc is longer than a turn-off time T1 of theswitch element SW1 when the switch element SW1 is turned off by thecontrol signal PWM_out.

Exemplary Operation of First Embodiment

FIG. 2 is a waveform diagram schematically illustrating an exemplaryoperation of the switch circuit 40 of FIG. 1 during a normal operation.A first graph of FIG. 2 shows a current Ids flowing through the switchelement SW1. Ith denotes a threshold of the overcurrent. A second graphof FIG. 2 shows the control signal DET_oc outputted from the overcurrentdetector circuit 2. A third graph of FIG. 2 shows a gate-source voltageVgs2 applied to the switch element SW2. Vth2 denotes a gate thresholdvoltage of the switch element SW2. A fourth graph of FIG. 2 shows agate-source voltage Vgs1 applied to the switch element SW1. Vth1 denotesa gate threshold voltage of the switch element SW1.

In the example of FIG. 2, since the current Ids is always equal to orsmaller than the threshold Ith (that is, an overcurrent has not occurredin the switch element SW1), the control signal DET_oc is kept at the lowlevel, and thus, the switch element SW2 is kept off. In this case, theswitch element SW1 operates according to the control signal PWM_outoutputted from the driver circuit 1 (referred to as a “normaloperation”). When the control signal PWM_out transitions from the lowlevel to the high level, the gate-source voltage Vgs1 of the switchelement SW1 starts to increase. Thereafter, when the gate-source voltageVgs1 exceeds the gate threshold voltage Vth1 (time t1), the switchelement SW1 is turned on, and the current Ids starts to flow. When thecontrol signal PWM_out transitions from the high level to the low level(time t2), the gate-source voltage Vgs1 starts to decrease. When anovercurrent has not occurred in the switch element SW1, that is, whenthe switch element SW2 is turned off, the switch element SW1 has a timeconstant determined by its capacitance (for example, a gate-sourcecapacitance) and the resistor R1. The gate-source voltage Vgs1 graduallydecreases over a time depending on the time constant of the switchelement SW1. When the gate-source voltage Vgs1 is equal to or smallerthan the gate threshold voltage Vth1 (time t3), the switch element SW1is turned off, and the current Ids starts to decrease. As describedabove, when an overcurrent has not occurred in the switch element SW1,that is, when the switch element SW2 is turned off, the switch elementSW1 has the turn-off time T1 from time t2 to time t3.

FIG. 3 is a waveform diagram schematically illustrating an exemplaryoperation of the switch circuit 40 of FIG. 1 when detecting anovercurrent. In a manner similar to that of FIG. 2, when the controlsignal PWM_out transitions from the low level to the high level, thegate-source voltage Vgs1 of the switch element SW1 starts to increase.Thereafter, when the gate-source voltage Vgs1 exceeds the gate thresholdvoltage Vth1 (time t11), the switch element SW1 is turned on, and thecurrent Ids starts to flow. In the example of FIG. 3, the current Idsbecomes larger than the threshold Ith at a time t12 (that is, anovercurrent has occurred in the switch element SW1), and accordingly,the control signal DET_oc transitions from the low level to the highlevel, and the gate-source voltage Vgs2 of the switch element SW2 startsto increase. When the gate-source voltage Vgs2 reaches the gatethreshold voltage Vth2 (time t13), the switch element SW2 is turned on,and the gate-source voltage Vgs1 of the switch element SW1 starts todecrease. When an overcurrent has occurred in the switch element SW1,that is, when the switch element SW2 is turned on, the switch elementSW1 has a time constant determined by a capacitance of the switchelement SW2 and the resistor R2, as well as the capacitance of theswitch element SW1 and the resistor R1. In a manner similar to that ofFIG. 2, the gate-source voltage Vgs1 gradually decreases over a timedepending on the time constant of the switch element SW1. When thegate-source voltage Vgs1 is equal to or smaller than the gate thresholdvoltage Vth1 (time t14), the switch element SW1 is turned off, and thecurrent Ids starts to decrease. As described above, when an overcurrenthas occurred in the switch element SW1, that is, when the switch elementSW2 is turned on, the switch element SW1 has the turn-off time T2 fromtime t13 to time t14. In addition, in this case, the switch element SW1is turned off by the switch element SW2 regardless of a state of thecontrol signal PWM_out (that is, even when the control signal PWM_out iskept at the high level).

As described above, the resistances of the resistors R1 and R2 are setsuch that the turn-off time T2 is longer than the turn-off time T1.Accordingly, when an overcurrent has occurred in the switch element SW1,the gate-source voltage Vgs1 of the switch element SW1 decreases moreslowly than during the normal operation, and the switch element SW1 isturned off using soft turn-off. By turning the switch element SW1 offusing soft turn-off, a voltage surge is less likely to occur in theswitch element SW1.

The turn-off times T1 and T2 can be individually set by adjusting theresistances of the resistors R1 and R2.

The resistance of the resistor R1 may be set to a small value in orderto operate the switch element SW1 at a desired switching speed duringthe normal operation. On the other hand, the resistance of the resistorR2 is set to a large value (for example, a value much larger than theresistance of the resistor R1) in order to turn the switch element SW1off using soft turn-off when an overcurrent has occurred in the switchelement SW1.

Conventionally, a circuit is known in which a gate terminal of a switchelement is connected to a driver circuit and an overcurrent protectioncircuit via first and second resistors different from each other. Forexample, ROHM Co., Ltd. supplies a gate driver BM6108FV-LBE2 for such acircuit. The gate driver BM6108FV-LBE2 is configured to have a built-indriver circuit and overcurrent protection circuit, and to externallyconnect the switch element and the resistors. In such a circuit, it isexpected to achieve the same operation as that of the switch circuitaccording to the present embodiment, by using the first and secondresistors having different resistances so that the turn-off time duringthe normal operation and the turn-off time when detecting theovercurrent are set to be different from each other. However, in such acircuit, it is not possible to actually achieve the same operation asthat of the switch circuit according to the present embodiment, asdescribed below.

FIG. 4 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit according to a comparison example. Theswitch circuit of FIG. 4 is provided with a resistor R3 connectedbetween the gate terminal G of the switch element SW1 and the drainterminal D of the switch element SW2, instead of the resistor R2 of theswitch circuit 40 of FIG. 1.

When the switch element SW2 is turned on, the gate-source voltage Vgs1of the switch element SW1 is given as follows.Vgs1=Vdr×R3/(R1+R3)

Where, Vdr denotes a voltage of the control signal PWM_out.

In order to turn the switch element SW1 off using soft turn-off, it isnecessary to set R1<<R3. Accordingly, the gate-source voltage Vgs1almost never decreases from the voltage Vdr as given in the followingmathematical expression, and the switch element SW1 cannot be turnedoff.Vdr×R3/(R1+R3)≈Vdr×R3/(R3)=Vdr

As described above, according to the switch circuit of FIG. 4, since thegate-source voltage Vgs1 of the switch element SW1 does not decreasebelow a voltage determined by a voltage division ratio of the resistorsR1 and R3, the switch element SW1 cannot be turned off, even when theswitch element SW2 is turned on. Accordingly, in the switch circuit ofFIG. 4, it is difficult to achieve the soft turn-off of the switchelement SW1.

On the other hand, according to the switch circuit 40 of the presentembodiment, when the switch element SW2 is turned off, the gate-sourcevoltage Vgs1 of the switch element SW1 decreases to the electricpotential of the ground GND. The switch element SW1 is turned off usingsoft turn-off at the turn-off time T2 depending on the resistance of theresistor R2. As described above, the switch circuit 40 according to thepresent embodiment is essentially different from the switch circuit ofthe comparison example.

Advantageous Effects of First Embodiment

According to the switch circuit 40 of the present embodiment, when anovercurrent has occurred in the switch element SW1, the switch elementSW2 forcibly turns the switch element SW1 off using soft turn-offregardless of the state of the control signal PWM_out. Accordingly, itis possible to safely protect the switch element SW1 from theovercurrent without being restricted by the state of the control signalPWM_out.

In addition, according to the switch circuit 40 of the presentembodiment, the drain terminal D of the switch element SW2 is directlyconnected to the gate terminal G of the switch element SW1. Since thereis no extra circuit element between the switch elements SW2 and SW1, adelay is less likely to occur in the operation from detection of anovercurrent to protection against the overcurrent.

In addition, according to the switch circuit 40 of the presentembodiment, since the switch element SW1 is directly turned off by theswitch element SW2, the overcurrent protection does not include amulti-stage operation. Accordingly, a delay is less likely to occur inthe operation from detection of an overcurrent to protection against theovercurrent.

In addition, the switch circuit 40 according to the present embodimentprotects the switch element SW1 from the overcurrent, using a small andsimple overcurrent protection circuit including the switch element SW2,the overcurrent detector circuit 2, and the resistor R2. Accordingly, itis possible to implement a small and low-cost switch circuit.

In addition, since the switch circuit 40 according to the presentembodiment achieves the overcurrent protection using a small and simplecircuit, it is possible to reduce the overall inductance of theovercurrent protection circuit and the switch circuit 40. Accordingly,even when driving a next-generation high-speed power semiconductorelement including SJMOS, SiC, GaN, etc., a large driving noise is lesslikely to occur.

In addition, according to the switch circuit 40 of the presentembodiment, when the switch element SW2 is turned off (that is, when anovercurrent has not occurred in the switch element SW1), the normaloperation of the switch element SW1 is not affected by the overcurrentprotection circuit, and no delay occurs due to the overcurrentprotection circuit. Accordingly, a decrease in the switching speed and aloss of the switch element SW1 during the normal operation are lesslikely to occur.

In addition, the switch circuit 40 according to the present embodimentcan be configured by externally connecting an overcurrent protectioncircuit to the generic driver circuit 1. Accordingly, the driver circuit1 may not have an extra function for overcurrent protection, and it ispossible to increase a degree of freedom in designing the switchcircuit.

As described above, according to the switch circuit 40 of the presentembodiment, it is possible to achieve overcurrent protection with acircuit smaller and simpler than that of the prior art, and with anoperation simpler than that of the prior art, without affecting a normaloperation.

Modified Embodiments of First Embodiment

Next, modified embodiments of the first embodiment will be describedwith reference to FIG. 5 to FIG. 13.

First Modified Embodiment of First Embodiment

FIG. 5 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit 40A according to a first modifiedembodiment of the first embodiment. The switch circuit 40A of FIG. 5 isprovided with a control circuit 30A, instead of the control circuit 30of FIG. 1. The control circuit 30A is provided with the components ofthe control circuit 30 of FIG. 1, and further provided with a capacitorC1 connected between the source terminal S and the gate terminal G ofthe switch element SW2.

The switch element SW2 has a mirror capacitance Cm between the drainterminal D and the gate terminal G. In the switch circuit 40 of FIG. 1,a mirror current may flow from the driver circuit 1 to the resistor R2via a mirror capacitance Cm of the switch element SW2 during the normaloperation. Accordingly, there is a problem that the gate-source voltageVgs2 of the switch element SW2 increases, and the switch element SW2 isfalsely turned on. Thus, in the switch circuit 40A in FIG. 5, thecapacitor C1 is added to prevent the gate-source voltage Vgs2 fromincreasing due to the mirror current.

Next, effects of providing the capacitor C1 will be described withreference to FIG. 6 and FIG. 7.

FIG. 6 is a circuit diagram schematically illustrating an exemplaryconfiguration of the switch circuit 40A of FIG. 5 for simulationthereof. A voltage source V1 was used as a signal source of the PWMsignal. A voltage source V2 was used as a signal source of the controlsignal DET_oc outputted from the overcurrent detector circuit 2. Avoltage source V3 of 450 V was used instead of the voltage source VDD ofFIG. 5. SCT2080KE which is a MOSFET supplied by ROHM Co., Ltd. was usedas the switch element SW1. RSR025N03 which is a MOSFET supplied by ROHMCo., Ltd. was used as the switch element SW2. The resistor R1 was 15Ω,and the resistor R2 was 930Ω. The capacitor C1 was 500 pF. SCT2080KE andan inductor of 50 μH were used as loads.

FIG. 7 is a waveform diagram schematically illustrating an exemplaryoperation of the switch circuit of FIG. 6. Simulations were performed ina case where the switch circuit of FIG. 6 is provided with the capacitorC1, and in a case where the switch circuit is not provided with thecapacitor C1. A first graph of FIG. 7 shows the current Ids flowingthrough the switch element SW1. A second graph of FIG. 7 shows thedrain-source voltage Vds1 applied to the switch element SW1. A thirdgraph of FIG. 7 shows the gate-source voltage Vgs2 applied to the switchelement SW2. A fourth graph of FIG. 7 shows the gate-source voltage Vgs1applied to the switch element SW1. According to the third graph of FIG.7, when the switch circuit is not provided with the capacitor C1, anoise more than 2 V occurs due to the mirror current at time of 3microseconds. Accordingly, there is a high possibility that the switchelement SW2 is falsely turned on. On the other hand, when the switchcircuit is provided with the capacitor C1, it can be seen that thisnoise is reduced by about half.

According to the switch circuit 40A of FIG. 5, since the capacitor C1 isprovided, a malfunction of the switch element SW2 due to the mirrorcurrent is less likely to occur.

Second Modified Embodiment of First Embodiment

FIG. 8 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit 40B according to a second modifiedembodiment of the first embodiment. The switch circuit 40B of FIG. 8 isprovided with a control circuit 30B instead of the control circuit 30 ofFIG. 1. The control circuit 30B is provided with the components of thecontrol circuit 30 of FIG. 1, and further provided with a level shifter3 connected between the overcurrent detector circuit 2 and the resistorR2. The level shifter 3 shifts an electric potential of the controlsignal DET_oc (or at least an electric potential of the control signalDET_oc at the low level) so as to have a polarity opposite to a polarityof the electric potential of the voltage source VDD (that is, negativeelectric potential), with respect to the electric potential of theground GND. According to the switch circuit 40B of FIG. 8, since thegate-source voltage Vgs2 of the switch element SW2 is shifted inadvance, the gate-source voltage Vgs2 is less likely to reach the gatethreshold Vth2, even when the mirror current flows via the mirrorcapacitance of the switch element SW2. Accordingly, a malfunction of theswitch element SW2 due to the mirror current is less likely to occur.

For example, assume that the control signal DET_oc is 20 V at the highlevel, and 0 V at the low level. The level shifter 3 may shift theelectric potential of the control signal DET_oc by, for example, −2 V.

The level shifter 3 may be integrated with the overcurrent detectorcircuit 2. In this case, when turning the switch element SW2 off, theovercurrent detector circuit 2 generates the control signal DET_ochaving a polarity opposite to a polarity of the electric potential ofthe voltage source VDD, with respect to the electric potential of theground GND.

The switch circuit may be provided with both the capacitor C1 of FIG. 5and the level shifter 3 of FIG. 8 so that a malfunction of the switchelement SW2 is less likely to occur.

Third Modified Embodiment of First Embodiment

FIG. 9 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit 40C according to a third modifiedembodiment of the first embodiment. The switch circuit 40C of FIG. 9 isprovided with a control circuit 30C instead of the control circuit 30 ofFIG. 1. The control circuit 30C is provided with a driver circuit 1C,instead of the driver circuit 1 and the resistor R1 of the controlcircuit 30 of FIG. 1. The driver circuit 1C has a resistor R1 integratedtherein. Accordingly, it is possible to further reduce the size of theswitch circuit and simplify the switch circuit, as compared with thecases of FIG. 1 and other drawings.

In the switch circuits of FIG. 1 and other drawings, at least onecomponent other than the resistor R1 may be integrated, or all thecomponents may be integrated. Accordingly, it is possible to furtherreduce the size of the switch circuit and simplify the switch circuit.

Fourth Modified Embodiment of First Embodiment

FIG. 10 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit 40D according to a fourth modifiedembodiment of the first embodiment. The switch circuit 40D of FIG. 10 isprovided with a control circuit 30D instead of the control circuit 30 ofFIG. 1. The control circuit 30D is provided with a PWM control circuit 4instead of the resistor R2 of FIG. 1. The PWM control circuit 4generates a PWM signal having a duty cycle variable depending on whetherthe control signal DET_oc outputted from the overcurrent detectorcircuit 2 is at the high level or the low level, and applies thegenerated PWM signal to the gate terminal G of the switch element SW2.By adjusting the duty cycle of the PWM signal, it is possible to adjustan amount of charge to the gate capacitance of the switch element SW2.Accordingly, an ON time of the switch element SW2 can be adjusted.According to the switch circuit 40D of FIG. 10, the size of the circuitcan be reduced by removing the resistor R2.

Fifth Modified Embodiment of First Embodiment

FIG. 11 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit 40E according to a fifth modifiedembodiment of the first embodiment. The switch circuit 40E of FIG. 11 isprovided with a control circuit 30E instead of the control circuit 30 ofFIG. 1. The control circuit 30E is provided with a switch element SW2Eand an overcurrent detector circuit 2E, instead of the switch elementSW2 and the overcurrent detector circuit 2 of FIG. 1.

The switch element SW2E is a source terminal S connected to the gateterminal G of the switch element SW1, a drain terminal D connected to aterminal having the same electric potential as the electric potential ofthe source terminal S of the switch element SW1 (in the example of FIG.11, the ground GND), and a gate terminal G. The switch element SW2E is aP-channel MOSFET.

The switch element SW2E is, herein, also referred to as the “secondswitch element”. In addition, herein, the source terminal S of theswitch element SW2E is also referred to as the “fourth terminal”, thedrain terminal D thereof is also referred to as the “fifth terminal”,and the gate terminal G thereof is also referred to as the “sixthterminal”. The switch element SW2E which is the P-channel MOSFET is anexample of the “second switch element”.

The overcurrent detector circuit 2E generates a control signal DET_ocfor turning the switch element SW2E on and off. In a case where theswitch element SW2E is the P-channel MOSFET as described above, theovercurrent detector circuit 2E sets the control signal DET_oc to a lowlevel when the current flowing through the switch element SW1 exceedsthe threshold Ith, and sets the control signal DET_oc to a high levelwhen the current flowing through the element SW1 is equal to or smallerthan the threshold Ith.

In other respects, the switch circuit 40E of FIG. 11 is configured andoperates in a manner similar to that of the switch circuit 40 of FIG. 1.

Switch elements with various specifications (N-channel type or P-channeltype) are available, and overcurrent detector circuits with variousspecifications (the control signal to be outputted upon detection of anovercurrent is set to the high level or the low level) are available.According to the switch circuits of FIG. 1 and other drawings, theovercurrent detector circuit can be appropriately selected according tothe specifications of the second switch element. In addition, accordingto the switch circuits of FIG. 1 and other drawings, the switch elementscan be appropriately selected according to the specifications of theovercurrent detector circuit.

Even when the second switch element is the P-channel MOSFET, it ispossible to achieve overcurrent protection with a circuit smaller andsimpler than that of the prior art, and with an operation simpler thanthat of the prior art, without affecting a normal operation, in a mannersimilar to that of the switch circuits of FIG. 1 and other drawings.

The switch circuit may be further provided with a logic inverter betweenthe overcurrent detector circuit and the second switch element, in orderto invert a logical value of the second control signal DET_oc accordingto the specification of the second switch element.

Sixth Modified Embodiment of First Embodiment

FIG. 12 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit 40F according to a sixth modifiedembodiment of the first embodiment. The switch circuit 40F of FIG. 12 isprovided with a switch element SW1F, a driver circuit 1F, a resistor R1,a switch element SW2F, an overcurrent detector circuit 2F, and aresistor R2. The switch element SW2F, the overcurrent detector circuit2F, and the resistor R2 constitute an overcurrent protection circuit forthe switch element SW1F, the overcurrent protection circuit detecting anovercurrent in the switch element SW1F, and protecting the switchelement SW1F from the overcurrent. In addition, the driver circuit 1F,the resistor R1, the switch element SW2F, the overcurrent detectorcircuit 2F, and the resistor R2 constitute a control circuit 30F for theswitch element SW1F, the control circuit 30F turning the switch elementSW1F on and off, detecting an overcurrent in the switch element SW1F,and protect the switch element SW1F from the overcurrent.

The switch element SW1F has a collector terminal C connected to avoltage source VCC, an emitter terminal E connected to a ground GND, anda base terminal B. The switch element SW1F is an NPN transistor. Anelectric potential of the voltage source VCC is higher than an electricpotential of the ground GND.

The switch element SW1F is, herein, also referred to as the “firstswitch element”. In addition, herein, the collector terminal C of theswitch element SW1F is also referred to as the “first terminal”, theemitter terminal E thereof is also referred to as the “second terminal”,and the base terminal B thereof is also referred to as the “thirdterminal”. In addition, herein, the voltage source VCC is also referredto as the “first voltage source”, and the ground GND is also referred toas the “second voltage source”. The voltage source VCC and the groundGND are examples of the “first voltage source” and the “second voltagesource”, respectively. In addition, the switch element SW1F which is theNPN transistor is an example of the “first switch element”.

The driver circuit 1F generates a control signal PWM_out for turning theswitch element SW1F on and off with a certain duty cycle. When theswitch element SW1F is the NPN transistor as described above, thecontrol signal PWM_out becomes a high level when turning the switchelement SW1F on, and the control signal PWM_out becomes a low level whenturning the switch element SW1F off.

The resistor R1 is connected between the driver circuit 1F and the baseterminal B of the switch element SW1F.

The switch element SW2F has a collector terminal C connected to the baseterminal B of the switch element SW1F, an emitter terminal E connectedto a terminal having the same electric potential as the electricpotential of the emitter terminal E of the switch element SW1F (in theexample of FIG. 12, the ground GND), and a base terminal B. The switchelement SW2F is an NPN transistor.

The switch element SW2F is, herein, also referred to as the “secondswitch element”. In addition, herein, the collector terminal C of theswitch element SW2F is also referred to as the “fourth terminal”, theemitter terminal E thereof is also referred to as the “fifth terminal”,and the base terminal B thereof is also referred to as the “sixthterminal”. The switch element SW2F which is the NPN transistor is anexample of the “second switch element”.

The overcurrent detector circuit 2F generates a control signal DET_ocfor turning the switch element SW2F on and off. When the switch elementSW2F is the NPN transistor as described above, the overcurrent detectorcircuit 2F sets the control signal DET_oc to a high level when thecurrent flowing through the switch element SW1F exceeds the thresholdIth, and sets the control signal DET_oc to a low level when the currentflowing through the switch element SW1F is equal to or smaller than thethreshold Ith.

The resistor R2 is connected between the overcurrent detector circuit 2Fand the base terminal B of the switch element SW2F.

In other respects, the switch circuit 40F of FIG. 12 is configured andoperates in a manner similar to that of the switch circuit 40 of FIG. 1.

Even when the second switch element is the NPN transistor, it ispossible to achieve overcurrent protection with a circuit smaller andsimpler than that of the prior art, and with an operation simpler thanthat of the prior art, without affecting a normal operation, in a mannersimilar to that of the switch circuits of FIG. 1 and other drawingsprovided with the N-channel or P-channel MOSFET.

Seventh Modified Embodiment of First Embodiment

FIG. 13 is a circuit diagram schematically illustrating an exemplaryconfiguration of a switch circuit 40G according to a seventh modifiedembodiment of the first embodiment. The switch circuit 40G of FIG. 13 isprovided with a control circuit 30G instead of the control circuit 30Fof FIG. 12. The control circuit 30G is provided with a switch elementSW2G and an overcurrent detector circuit 2G, instead of the switchelement SW2F and the overcurrent detector circuit 2F of FIG. 12.

The switch element SW2G has an emitter terminal E connected to the baseterminal B of the switch element SW1F, a collector terminal C connectedto a terminal having the same electric potential as the electricpotential of the emitter terminal E of the switch element SW1F (in theexample of FIG. 13, the ground GND), and a base terminal B. The switchelement SW2G is a PNP transistor.

The switch element SW2G is, herein, also referred to as the “secondswitch element”. In addition, herein, the emitter terminal E of theswitch element SW2G is also referred to as the “fourth terminal”, thecollector terminal C thereof is also referred to as the “fifthterminal”, and the base terminal B thereof is also referred to as the“sixth terminal”. The switch element SW2G which is the PNP transistor isan example of the “second switch element”.

The overcurrent detector circuit 2G generates a control signal DET_ocfor turning the switch element SW2G on and off. When the switch elementSW2G is the PNP transistor as described above, the overcurrent detectorcircuit 2G sets the control signal DET_oc to the low level when thecurrent flowing through the switch element SW1F exceeds the thresholdIth, and sets the control signal DET_oc to the high level when thecurrent flowing through the switch element SW1F is equal to or smallerthan the threshold Ith.

In other respects, the switch circuit 40G of FIG. 13 is configured andoperates in a manner similar to that of the switch circuit 40F of FIG.12.

Even when the second switch element is the PNP transistor, it ispossible to achieve overcurrent protection with a circuit smaller andsimpler than that of the prior art, and with an operation simpler thanthat of the prior art, without affecting a normal operation, in a mannersimilar to that of the switch circuits of FIG. 1 and other drawings.

The first switch circuit which is the N-channel MOSFET may be combinedwith the second switch circuit which is the NPN or PNP transistor. Inaddition, the first switch circuit which is the NPN transistor may becombined with the second switch circuit which is the N-channel orP-channel MOSFET.

Second Embodiment

Power converter apparatuses according to a second embodiment will bedescribed with reference to FIG. 14 to FIG. 17.

Exemplary Configuration of Second Embodiment

FIG. 14 is a block diagram schematically illustrating an exemplaryconfiguration of a power system according to the second embodiment. Thepower system of FIG. 14 is provided with a power generator apparatus 11,a power storage apparatus 12, an electric vehicle 13, a commercial powersystem 14, and power converter apparatuses 21 to 24.

The power generator apparatus 11 generates a DC power, and sends the DCpower to the power converter apparatus 21. The power generator apparatus11 is, for example, a solar cell, but is not limited thereto.

The power converter apparatus 21 converts inputted DC power at a certainvoltage, into DC power at a higher voltage for output. In the example ofFIG. 14, the power converter apparatus 21 sends the converted DC powerto the power converter apparatuses 22 to 24.

Each of the power converter apparatuses 22 and 23 converts inputted DCpower at a certain voltage, into DC power at a lower voltage for output.In the example of FIG. 14, the power converter apparatuses 22 and 23send the converted DC power to the power storage apparatus 12 and theelectric vehicle 13, respectively.

The power storage apparatus 12 stores inputted power. The electricvehicle 13 stores inputted power in an internal battery.

The power converter apparatus 24 converts inputted DC power into ACpower for output. The power converter apparatus 24 sends the convertedAC power to the commercial power system 14.

FIG. 15 is a block diagram schematically illustrating an exemplaryconfiguration of the power converter apparatus 21 of FIG. 14. The powerconverter apparatus 21 is provided with a switch circuit 41, an inductorL11, and a diode D1. The switch circuit 41 is provided with a switchelement SW11 and a control circuit 31. The switch element SW11corresponds to the first switch element of FIG. 1 and other drawings.The control circuit 31 is provided with components corresponding to thecomponents other than the first switch element of FIG. 1 and otherdrawings. In the control circuit 31, the source terminal (or the emitterterminal) of the second switch element is connected to the sourceterminal S of the switch element SW11. The control circuit 31 turns theswitch element SW11 on and off, detects an overcurrent in the switchelement SW11, and protects the switch element SW11 from the overcurrent,in a manner similar to that of the control circuit for the first switchelement of FIG. 1 and other drawings.

FIG. 16 is a block diagram schematically illustrating an exemplaryconfiguration of the power converter apparatus 22 of FIG. 14. The powerconverter apparatus 22 is provided with a switch circuit 42 and aninductor L12. The switch circuit 42 is provided with switch elementsSW12 and SW13, and a control circuit 32. Each of the switch elementsSW12 and SW13 corresponds to the first switch element of FIG. 1 andother drawings. The control circuit 32 is provided with componentscorresponding to the components other than the first switch element ofFIG. 1 and other drawings, for each of the switch elements SW12 andSW13. In the control circuit 32, the source terminal (or the emitterterminal) of the second switch element for the switch element SW12 isconnected to the source terminal S of the switch element SW12. Inaddition, in the control circuit 32, the source terminal (or the emitterterminal) of the second switch element for the switch element SW13 isconnected to the source terminal S of the switch element SW13. Thecontrol circuit 32 turns the switch element SW12 on and off, detects anovercurrent in the switch element SW12, protects the switch element SW12from the overcurrent, and further turns the switch element SW13 on andoff, detects an overcurrent in the switch element SW13, and protects theswitch element SW13 from the overcurrent, in a manner similar to that ofthe control circuit for the first switch element of FIG. 1 and otherdrawings.

The power converter apparatus 23 of FIG. 14 is also configured in amanner similar to that of the power converter apparatus 22 of FIG. 16.

FIG. 17 is a block diagram schematically illustrating an exemplaryconfiguration of the power converter apparatus 24 of FIG. 14. The powerconverter apparatus 24 is provided with a switch circuit 43, inductorsL13 and L14, and a capacitor C11. The switch circuit 43 is provided withswitch elements SW14 to SW17 and a control circuit 33. Each of theswitch elements SW14 to SW17 corresponds to the first switch element ofFIG. 1 and other drawings. The control circuit 33 is provided withcomponents corresponding to the components other than the first switchelement of FIG. 1 and other drawings, for each of the switch elementsSW14 to SW17. In the control circuit 33, the source terminal (or theemitter terminal) of the second switch element for the switch elementSW14 is connected to the source terminal S of the switch element SW14.In addition, in the control circuit 33, the source terminal (or theemitter terminal) of the second switch element for the switch elementSW15 is connected to the source terminal S of the switch element SW15.In addition, in the control circuit 33, the source terminal (or theemitter terminal) of the second switch element for the switch elementSW16 is connected to the source terminal S of the switch element SW16.In addition, in the control circuit 33, the source terminal (or theemitter terminal) of the second switch element for the switch elementSW17 is connected to the source terminal S of the switch element SW17.The control circuit 33 turns the switch element SW14 on and off, detectsan overcurrent in the switch element SW14, protects the switch elementSW14 from the overcurrent, turns the switch element SW15 on and off,detects an overcurrent in the switch element SW15, protects the switchelement SW15 from the overcurrent, turns the switch element SW16 on andoff, detects an overcurrent in the switch element SW16, protects theswitch element SW16 from the overcurrent, turns the switch element SW17on and off, detects an overcurrent in the switch element SW17, andprotects the switch element SW17 from the overcurrent, in a mannersimilar to that of the control circuit for the first switch element ofFIG. 1 and other drawings.

The power converter apparatus 24 may be further provided with atransformer for changing a voltage of the converted AC power.

According to the power converter apparatuses 21 to 24 of FIG. 14, sincethe control circuits 31 to 33 are provided, it is possible to achieveovercurrent protection with a circuit smaller and simpler than that inthe prior art, and with an operation simpler than that in the prior art,without affecting a normal operation.

Although the switch elements SW11 to SW17 are shown as the N-channelMOSFETs in FIG. 15 to FIG. 17, the switch elements SW11 to SW17 may bethe NPN transistors.

Other Modified Embodiments

Although the embodiments of the present disclosure have been describedin detail above, the above descriptions are merely examples of thepresent disclosure in all respects. Needless to say, variousimprovements and modifications can be made without departing from thescope of the present disclosure. For example, the following changes canbe made. Hereinafter, components similar to those of the aboveembodiments are indicated by similar reference signs, and points similarto those of the above embodiments will be omitted as appropriate.

The above-described embodiments and modified embodiments may be combinedin any combination.

The embodiments described herein are merely examples of the presentdisclosure in all respects. Needless to say, various improvements andmodifications can be made without departing from the scope of thepresent disclosure. That is, specific configurations corresponding tothe embodiments may be appropriately adopted in implementing the presentdisclosure.

Summary of Embodiments

The switch circuit and the power converter apparatus according to eachaspect of the present disclosure may be expressed as follows.

A switch circuit (40, 40A to 40G, 41 to 43) according to a first aspectof the present disclosure is provided with: a first switch element (SW1,SW1F), a first resistor (R1), a driver circuit (1, 1C, 1F), a secondswitch element (SW2, SW2E to SW2G), an overcurrent detector circuit (2,2E to 2G), and a second resistor (R2). The first switch element (SW1,SW1F) has a first terminal connected to a first voltage source (VDD,VCC), a second terminal connected to a second voltage source (GND), anda third terminal. The driver circuit (1, 1C, 1F) that generates a firstcontrol signal for turning the first switch element (SW1, SW1F) on andoff. The first resistor (R1) is connected between the driver circuit (1,1C, 1F) and the third terminal. The second switch element (SW2, SW2E toSW2G) has a fourth terminal connected to the third terminal, a fifthterminal connected to the second voltage source (GND), and a sixthterminal. The overcurrent detector circuit (2, 2E to 2G) generates asecond control signal for turning the second switch element (SW2, SW2Eto SW2G) on and off, based on whether or not a current flowing throughthe first switch element (SW1, SW1F) exceeds a predetermined threshold.The second resistor (R2) is connected between the overcurrent detectorcircuit (2, 2E to 2G) and the sixth terminal. The first and secondresistors (R1, R2) have resistances set such that a turn-off time of thefirst switch element (SW1, SW1F) when the second switch element (SW2,SW2E to SW2G) is turned on by the second control signal is longer than aturn-off time of the first switch element (SW1, SW1F) when the firstswitch element (SW1, SW1F) is turned off by the first control signal.

A switch circuit (40A) according to a second aspect of the presentdisclosure is configured in a manner similar to that of the switchcircuit according to the first aspect, and the switch circuit (40A) isfurther provided with a capacitor (C1) that is connected between thefifth and sixth terminals of the second switch element (SW2).

A switch circuit (40B) according to a third aspect of the presentdisclosure is configured in a manner similar to that of the switchcircuit according to the first or second aspect, and in the switchcircuit (40B), when turning the second switch element (SW2) off, theovercurrent detector circuit (2, 3) generates the second control signalhaving a polarity opposite to a polarity of an electric potential of thefirst voltage source (VDD), with respect to an electric potential of thesecond voltage source (GND).

A switch circuit (40C) according to a fourth aspect of the presentdisclosure is configured in a manner similar to that of the switchcircuit according to any one of the first to third aspects, and thefirst resistor (R1) is integrated with the driver circuit (1C).

A switch circuit (40, 40F) according to a fifth aspect of the presentdisclosure is configured in a manner similar to that of the switchcircuit according to any one of the first to fourth aspects, and in theswitch circuit (40, 40F), the second switch element (SW2, SW2F) is anNPN transistor or an N-channel MOSFET. The overcurrent detector circuit(2, 2F) sets the second control signal to a high level when the currentflowing through the first switch element (SW1, SW1F) exceeds thethreshold, and sets the second control signal to a low level when thecurrent flowing through the first switch element (SW1, SW1F) is equal toor smaller than the threshold.

A switch circuit (40E, 40G) according to a sixth aspect of the presentdisclosure is configured in a manner similar to that of the switchcircuit according to any one of the first to fourth aspects, and in theswitch circuit (40E, 40G), the second switch element (SW2E, SW2G) is aPNP transistor or a P-channel MOSFET. The overcurrent detector circuit(2E, 2G) sets the second control signal to a low level when the currentflowing through the first switch element (SW1F) exceeds the threshold,and sets the second control signal to a high level when the currentflowing through the first switch element (SW1F) is equal to or smallerthan the threshold.

A power converter apparatus according to a seventh aspect of the presentdisclosure is provided with at least one of the switch circuit (40, 40Ato 40G, 41 to 43) according to any one of the first to sixth aspects.

INDUSTRIAL APPLICABILITY

The switch circuit according to each aspect of the present disclosure isapplicable to, for example, overcurrent protection of switch elements ina power converter apparatus.

The switch circuit according to each aspect of the present disclosure isapplicable not only to the power converter apparatus, but also to anydevice requiring overcurrent protection.

The invention claimed is:
 1. A switch circuit comprising: a first switchelement that has a first terminal connected to a first voltage source, asecond terminal connected to a second voltage source, and a thirdterminal; a driver circuit that generates a first control signal forturning the first switch element on and off; a resistor that isconnected between the driver circuit and the third terminal; a secondswitch element that has a fourth terminal connected to the thirdterminal, a fifth terminal connected to the second voltage source, and asixth terminal; an overcurrent detector circuit that generates a secondcontrol signal based on whether or not a current flowing through thefirst switch element exceeds a predetermined threshold; and a PWMcontrol circuit that is connected between the overcurrent detectorcircuit and the sixth terminal, and generates a PWM signal for turningthe second switch element on and off, the PWM signal having a variableduty cycle depending on the second control signal, wherein the dutycycle of the PWM signal is adjusted so as to adjust an ON time of thesecond switch element.
 2. The switch circuit as claimed in claim 1,further comprising a capacitor that is connected between the fifth andsixth terminals of the second switch element.
 3. The switch circuit asclaimed in claim 1, wherein, when turning the second switch element off,the overcurrent detector circuit generates the second control signalhaving a polarity opposite to a polarity of a potential of the firstvoltage source, with respect to a potential of the second voltagesource.
 4. The switch circuit as claimed in claim 1, wherein theresistor is integrated with the driver circuit.
 5. The switch circuit asclaimed in claim 1, wherein the second switch element is an NPNtransistor or an N-channel MOSFET, and wherein the overcurrent detectorcircuit sets the second control signal to a high level when the currentflowing through the first switch element exceeds the threshold, and setsthe second control signal to a low level when the current flowingthrough the first switch element is equal to or smaller than thethreshold.
 6. The switch circuit as claimed in claim 1, wherein thesecond switch element is a PNP transistor or a P-channel MOSFET, andwherein the overcurrent detector circuit sets the second control signalto a low level when the current flowing through the first switch elementexceeds the threshold, and sets the second control signal to a highlevel when the current flowing through the first switch element is equalto or smaller than the threshold.
 7. A power converter apparatuscomprising at least one switch circuit, the at least one switch circuitcomprising: a first switch element that has a first terminal connectedto a first voltage source, a second terminal connected to a secondvoltage source, and a third terminal; a driver circuit that generates afirst control signal for turning the first switch element on and off; aresistor that is connected between the driver circuit and the thirdterminal; a second switch element that has a fourth terminal connectedto the third terminal, a fifth terminal connected to the second voltagesource, and a sixth terminal; an overcurrent detector circuit thatgenerates a second control signal based on whether or not a currentflowing through the first switch element exceeds a predeterminedthreshold; and a PWM control circuit that is connected between theovercurrent detector circuit and the sixth terminal, and generates a PWMsignal for turning the second switch element on and off, the PWM signalhaving a variable duty cycle depending on the second control signal,wherein the duty cycle of the PWM signal is adjusted so as to adjust anON time of the second switch element.